1. Field of the Invention
The present invention relates generally to CDMA mobile communication systems, and in particular, to a device and method for performing gated transmission (or intermittent transmission) in a control hold state.
2. Description of the Related Art
A conventional Code Division Multiple Access (CDMA) mobile communication system based on the IS-95 standard primarily supports a voice service. However, a mobile communication system in accordance with the IMT-2000 standard will support not only the voice service, but also a high-speed data transfer service. For example, the IMT-2000 standard can support a high-quality voice service, a moving picture service, an Internet search service, etc.
In a mobile communication system, a data communication service is characterized in that transmissions of burst data alternate with long non-transmission periods. Therefore, for the data communication service, a mobile communication system employs a channel assignment method in which a dedicated channel is assigned for only the data transmission duration. That is, taking into consideration the limited radio resources, base station capacity and power consumption of a mobile station, the mobile communication system connects a traffic channel and a control channel only for an actual data transmission duration and otherwise releases the dedicated channels (i.e., the traffic channel and the control channel) when there is no data to transmit for a predetermined time. When the dedicated channels are released, communication is performed through a common channel, thus increasing utility efficiency of the radio resources.
A conventional CDMA mobile communication system which mainly supports the voice service, releases a traffic channel upon completion of data transmission and then, reconnects the traffic channel when it is required to transmit data. However, the conventional channel assignment method is not suitable for a packet data service because of a time delay for reconnection of the channel. Therefore, to provide the packet data service as well as the voice service, there is required a new channel assignment method.
In general, during the packet data service, data transmission occurs intermittently. Therefore, a transmission duration of packet data alternates with periods of non-transmission. The mobile communication system either releases or maintains a channel in use for the periods of non-transmission, However, there are drawbacks associated with both maintaining and releasing a channel, namely, release of the channel causes an increase in service time due to a time delay for reconnection of the channel, and maintaining the channel causes a waste of the channel resources.
To solve these problems, there is proposed a method in which a dedicated control channel is provided between a base station and a mobile station to exchange traffic channel-related control signals over the dedicated control channel for the data transmission duration; and release the traffic channel and maintain only the dedicated control channel for the non-transmission duration. In this manner, the mobile communication system can prevent a waste of the channel resources and rapidly reconnect the traffic channel when there is data to transmit. The operating state described above is called a control hold state.
The mobile communication system includes additional operating states according to the channel assignment. FIG. 10 illustrates a state transition diagram of a mobile communication system for the packet service.
As shown in FIG. 10, for the packet service, the state transition diagram for the packet service illustrates a packet null state, an initialization state, an active state, a control hold state, a suspended state, a dormant state and a reconnect state. In the control hold, active and suspended states, a service option is connected and in the other states, the service option is not connected.
Further, the control hold state can be divided into a normal substate and a slotted substate], as shown in FIG. 11. The normal substate refers to a state where there is no data to transmit over a traffic channel and only a control signal is exchanged over a dedicated control channel. When the normal substate continues for a predetermined time, (i.e., when only the control signal is exchanged for a predetermined time without transmission of data), a transition to the slotted substate occurs. The slotted substate refers to a state where connection of the dedicated control channel is maintained but no control signal is exchanged over the dedicated control channel to reduce power consumption of a mobile station. However, to make a transition from the slotted substate to the normal substate to restart data transmission, resynchronization should be performed between a base station and a mobile station, since no control signal is exchanged between the base station and the mobile station in the slotted substate.
A reference will now be made to a base station and a mobile station for the conventional CDMA communication system which performs the above operations. FIG. 1A illustrates a conventional base station transmitter in a CDMA communication system.
With regard to forward link channels, the base station includes a pilot channel for sync acquisition and channel estimation, a forward common control channel (F-CCH) for communicating a control message in common to all the mobile stations located in a cell (or service) area of the base station, a forward dedicated control channel (F-DCCH) for exclusively communicating a control message to a specific mobile station located in the cell area of the base station, and a forward dedicated traffic channel (F-DTCH) for exclusively communicating traffic data (i.e., voice and packet data) to a specific mobile station located in the cell area of the base station. The forward dedicated control channel includes a sharable forward dedicated control channel (sharable F-DCCH) for exclusively communicating a control message to a specific mobile station by time slot multiplexing. The forward dedicated traffic channel includes a forward fundamental channel (F-FCH) and a forward supplemental channel (F-SCH).
Demultiplexers 120, 122, 124 and 126 demultiplex corresponding channel-coded interleaved channel information to I and Q channels. Here, serial-to-parallel converters can be used for the demultiplexers 120, 122, 124 and 126. It is assumed herein that signals input to the demultiplexers 120, 122, 124 and 126 are signal-mapped signals. Mixers 110, 130, 131, 132, 133, 134, 135, 136 and 137 multiply signals output from the associated demultiplexers by orthogonal codes assigned to the corresponding channels to orthogonally spread the signals output from the associated demultiplexers. Here, each of the mixers 110 and 130-137 serves as an orthogonal modulator. The orthogonally spread signals output from the mixers 130-137 are gain controlled by associated amplifiers 140-147.
Signals output from the amplifiers 140-147 and the mixer 110 are summed by summers 150 and 152 according to the I and Q channels. Since the signals applied to the summers 150 and 152 were channel separated by the orthogonal codes, the respective channel signals are orthogonal to one another. Outputs of the summers 150 and 152 are multiplied by PN (Pseudo Noise) sequences PN#I and PN#Q assigned to the base station for base station identification in a complex multiplier 160.
I and Q channel signals output from the complex multiplier 160 are applied to filters 170 and 171, respectively, which bandpass filter the input signals to output bandwidth-suppressed signals. The outputs of the filters 170 and 171 are amplified by amplifiers 172 and 173. Mixers 174 and 175 multiply outputs of the amplifiers 172 and 173 by a carrier cos(2xcfx80fct) to up-convert the signals to radio frequency (RF) signals. A summer 180 sums the I and Q channel signals.
FIG. 1B illustrates a conventional mobile station transmitter for the conventional CDMA communication system. With regard to reverse link channels, the mobile station includes a pilot/PCB (Power Control Bit) channel for multiplexing a pilot channel for sync acquisition and channel estimation and a forward power control bit for forward power control, a reverse dedicated control channel (R-DCCH) for exclusively communicating a control message to a base station, in a cell area of which the mobile station is located, and a reverse dedicated traffic channel (R-DTCH) for exclusively communicating traffic data to the base station. Further, the reverse dedicated traffic channel includes a reverse fundamental channel (R-FCH) and a reverse supplemental channel (R-SCH).
A multiplexer 210 multiplexes a signal on the reverse pilot channel and a power control bit for controlling power of the forward link. Mixers 220, 230, 240, 250 and 260 multiply corresponding channel-coded interleaved signals received over the respective reverse channels by orthogonal codes assigned to the corresponding channels to generate orthogonally spread signals for the respective channels. Outputs of the mixers 220, 240, 250 and 260 are gain controlled by amplifiers 222, 242, 252 and 262, respectively.
A summer 224 sums outputs of the amplifiers 222 and 242 and an output of the multiplier 230, and a summer 254 sums outputs of the amplifiers 252 and 262. Since the signals applied to the summers 224 and 254 were channel separated by the orthogonal codes, the respective channel signals are orthogonal to one another. A complex spreader (or complex multiplier) 160 multiplies signals output from the summers 224 and 254 by a spreading code assigned to the mobile station to spread the signals. The spreading code assigned to the mobile station is generated by mixing a PN sequence for a base station, in the cell area of which the mobile station is located, by a unique long code for the mobile station. Filters 170 and 171 filter I and Q channel signals output from the complex spreader 160, respectively, to generate bandwidth suppressed signals. Amplifiers 172 and 173 amplify outputs of the filters 170 and 171, respectively. Mixers 174 and 175 multiply signals output from the amplifiers 172 and 173 by a carrier cos(2fxcfx80ct) to up-convert the transmission signals to RF signals. A summer 180 sums the I and Q channel signals output from the mixers 174 and 175.
In the control hold state of the conventional CDMA communication system, a dedicated traffic channel is released and a control signal is communicated over a dedicated control channel. A description will be provided regarding the operation of a reverse pilot/PCB channel in the control hold state. Herein, it is assumed that the control hold state is divided into a normal substate and a slotted substate. However, even in the case where the control hold state is not divided into the normal substate and the slotted substate, the reverse pilot/PCB channel will have the same operation.
First, a mobile station constantly transmits a signal on the reverse pilot/PCB channel in order to avoid resync acquisition performed at a base station during a transition from the control hold state/normal substate (i.e., a normal substate of the control hold state) to the active state in a conventional CDMA communication system. The reverse pilot/PCB channel discontinues transmission only when a transition to the control hold state/slotted substate (i.e., a slotted substate of the control hold state) occurs. However, the signal on the reverse pilot/PCB channel is continuously transmitted until the occurrence of the transition to the slotted substate occurs, thereby increasing interference of a reverse link in the normal substate of the control hold state. The increase in interference of the reverse link inevitably decreases a capacity of the reverse link. Further, the unnecessary continuous transmission of the control signal causes an increase in power consumption.
Second, a description will be made regarding an operation for generating a reverse dedicated control channel (R-DCCH) when a reverse dedicated MAC (Medium Access Control) channel is generated in the conventional control hold state/normal substate. Logical channels for the reverse dedicated control channel include a dedicated MAC channel (dmch), a dedicated signaling channel (dsch) and a dedicated traffic channel (dtch). The dsch and dtch each have a 20 ms frame and the dmch has a 5 ms frame. Therefore, after generation of the dmch, an R-DCCH can be transmitted within 5 ms in maximum. Accordingly, the R-DCCH can be transmitted to locations which correspond to multiples of 5 ms. Therefore, when the dmch is transmitted, the base station may determine the existence of the R-DCCH only at four locations within one frame. However, after generation of the dmch, the R-DCCH is transmitted with a time delay of 5 ms in maximum. The dmch has 2.5 ms transmission delay on the average.
Third, in the case where reverse power control bits are disposed at fixed locations on a forward channel when the R-DCCH is not activated in the conventional control hold state/normal substate, both forward power control and reverse power control are performed at the same periods. Further, in the case where the reverse power control bits are disposed at variable locations within a power control group on the forward channel when the R-DCCH is not activated in the conventional control hold state/normal substate, both reverse power control and forward power control are performed at the same periods.
As stated above, the continuous transmission of the reverse pilot/PCB channel in the conventional control hold state/normal substate is advantageous in that the base station can avoid the resync acquisition procedure. However, the continuous transmission increases interference of the reverse link, causing a reduction in capacity of the reverse link. Further, continuous transmission of the reverse power control bits over the forward link causes an increase in interference of the forward link and a decrease in capacity of the forward link. In addition, the continuous transmission of the reverse power control bits may increase power consumption.
Therefore, there is a need for a method capable of suppressing unnecessary transmission of a control signal in the control hold state so as to (1) minimize resync acquisition time; (2) minimize interference due to transmission of the reverse pilot/PCB channel; and (3) minimize interference due to transmission of reverse power control bits over the forward link.
It is, therefore, an object of the present invention to provide a device and method for suppressing the unnecessary transmission of a control signal in a control hold state in a CDMA communication system.
It is another object of the present invention to provide a device and method for performing gated transmission by intermittently transmitting a control signal in a control hold state in a CDMA communication system.
It is a further object of the present invention to provide a device and method for receiving a control signal transmitted intermittently in a control hold state in a CDMA communication system.
It is a still further object of the present invention to provide a device and method for intermittently transmitting a control signal on a power control group unit basis in a control hold state in a CDMA communication system.
It is yet another object of the present invention to provide a device and method for intermittently transmitting a control signal on a time slot unit basis in a control hold state in a CDMA communication system.
It is a still further object of the present invention to provide a device and method for intermittently transmitting a control signal on a frame unit basis in a control hold state in a CDMA communication system.
It is another object of the present invention to provide a device and method for controlling transmission power in the case where reverse power control bits are disposed at fixed locations, when a reverse dedicated control channel is activated in a control hold state in a CDMA communication system which intermittently transmits a control signal.
It is a further object of the present invention to provide a device and method for controlling transmission power in the case where reverse power control bits are disposed at variable locations within a power control group, when a reverse dedicated control channel is activated in a control hold state in a CDMA communication system which intermittently transmits a control signal.
It is yet another object of the present invention to provide a device and method for transmitting a reverse power control command for multiple reverse channels in a control hold state in a CDMA communication system which intermittently transmits a control signal.
It is another object of the present invention to provide a device and method for generating a reverse transmission signal to implement a time diversity in transmitting traffic data using a reverse dedicated control channel in a control hold state in a CDMA communication system which intermittently transmits a control signal.
It is yet another object of the present invention to provide a device and method for generating a transmission signal to implement a time diversity in transmitting traffic data using a forward dedicated control channel in a control hold state in a CDMA communication system which intermittently transmits a control signal.
It is yet another object of the present invention to provide a device and method for performing gated transmission when there is no user data to transmit.
It is yet another object of the present invention to provide a device and method for intermittently transmitting a signal required to maintain a channel so as to maintain a state of the channel with a minimum signal at a duration where there is no data to exchange in a CDMA mobile communication system.
In accordance with one aspect of the present invention, a transmission device for a mobile station in a CDMA communication system includes a channel signal generator for generating a pilot channel signal for a reverse link, and a gating controller for intermittently transmitting the pilot channel signal generated from the channel signal generator according to a predetermined gating rate in a control hold state. The transmission device further includes a dedicated control channel signal generator for puncturing a control message to be transmitted and inserting power control information for controlling transmission power of a reverse link in the punctured message, and a gating controller for intermittently transmitting the power control information from the dedicated control channel generator according to a predetermined gating rate in a control hold state.